Cold sores can be triggered by a number of different things including illness, a weak immune system, changing hormone levels, or even stress.
Other triggers of cold sores are exposure to cold wind, exposure to hot sun or even just having a cold virus.
The cold sores are caused by the herpes simplex virus so you have to catch the herpes simplex virus to get a cold sore.
You can also spread a cold sore to someone else if you kiss that person because the virus that causes cold sores can transfer from you to them.
Then they get infected with the herpes simplex virus which causes the cold sores.
Cold sores usually go away on their own within 1 to 2 weeks.
But you can help get rid of the cold sore by applying some toothpaste, hydrogen peroxide, ice or even apple cider vinegar to the cold sore.